Remote control of home appliances, such as air conditioners and televisions, generally makes use of infrared communications (IR communications), wherein an infrared control signal (IR signal) is transmitted from a remote control transmitter to the home appliance via infrared rays. However, wireless radio communications (RF communications) systems, wherein control data are carried on a radio frequency (RF) signal that is not constrained by the transmission direction and can be transmitted even if an object is interposed in the transmission path, has been drawing attention in recent years.
With an RF communications system, the remote control transmitter transmits an RF signal of a specified frequency that has been modulated with control data, after which a controlled apparatus inputs just the RF signal of a specified frequency by passing the reception signal through a bandpass filter, and then responds in accordance with the control data that are demodulated from the RF signal.
Here, the transmission channel of the RF signal transmitted from the remote control transmitter and the reception channel on which the controlled apparatus receives the RF signal are made to coincide with a channel of a common frequency band. However, because the communication environment changes, there are times when a fixed channel cannot be used. An RF communications system is known in the conventional art as described in Japanese Published Unexamined Patent Application No. H08-265823, which is incorporated by reference herein in its entirety. The RF communication system as described by the '823 Application adopts a multiscan access method wherein the transmitter that transmits the RF signal searches for a channel with low electric field intensity, notifies the receiver of that channel, and uses it as the common channel.
The procedure that uses a common channel as recited in the '823 Application will now be explained, referencing FIG. 9. The transmitter that is about to transmit an RF signal: retrieves the previously used channel (step S101); examines the electric field intensity of that channel (step S102); if the electric field is strong, determines that the channel is unavailable, adds an appropriate number of channels, and sets a new channel (step S103); and once again examines the electric field intensity of that channel (step S102). This procedure is performed repetitively until a channel with low electric field is obtained. At first, the previously used channel is retrieved because there is a strong possibility that, unless there has been a change in the communication environment, the frequency band of that channel has a weak electric field.
If a channel with a weak electric field is obtained, then the RF signal is transmitted to the receiver on that channel (step S104). Moreover, the receiver stands by while performing a reception scan of all channels that can potentially be used by the transmitter, receives the RF signal transmitted from the abovementioned transmitter, and thereby sets the reception channel to that channel and transmits a response signal to the transmitter on that channel. If the transmitter does not obtain a response signal from the receiver within a prescribed time period, it considers that communication with the receiver could not be established and therefore repeats the procedure once again from step S101 (step S105); however, if a response signal is received within the prescribed time period (step S106), then the transmitter considers that communication with the receiver has been established, stores the channel at that time as the working channel (step S107), and establishes RF communications with the receiver using that channel as the working channel that is in common with the receiver (step S108).
Nevertheless, the method discussed above, wherein RF communications is established with a communication counterpart via the multiscan method, requires a procedure that demands a response signal from the communication counterpart, and is therefore unpreferable because that procedure is complicated in an RF communications system that remotely controls a controlled apparatus, such as a home appliance, with a remote control transmitter.
In addition, in order to examine the electric field intensity of all channels in the available frequency band on the transmitter side and to receive an RF signal transmitted from the transmitter on the receiver side, both the transmitter and the receiver must perform a reception scan of all channels so as to detect the RF signal, and therefore it takes time to establish communication and the overall configuration of each apparatus becomes complicated.
Furthermore, with the RF communications system that remotely controls the controlled apparatus with the remote control transmitter, the controlled apparatus should receive the RF signal transmitted from the remote control transmitter, and therefore, despite the need to set the reception channel to a channel for which the electric field intensity is low at the location of the controlled apparatus, which is on the receiver side, the abovementioned conventional art sets the common working channel to a channel for which the electric field intensity is low in the vicinity of the transmitter, which makes communication prone to reception errors at the controlled apparatus. In particular, in contrast with the controlled apparatus, which is at a fixed position and is in a reception environment that does not change greatly, if the remote control transmitter approaches a source that generates strong electromagnetic waves, such as a microwave oven, then there are cases wherein the optimal channel for RF communications cannot be selected with the conventional method that searches for a channel with low electric field intensity at the location of the remote control transmitter.
In addition, because of the demand to reduce costs, conventional controlled apparatuses that operate by receiving infrared control signals often incorporate an IR communications system dedicated microcontroller that is equipped just with a pulse modulated signal input port, such as a PWM input port, that inputs a pulse modulated signal demodulated from the infrared control signal. However, in order to control a controlled apparatus that is equipped with such a microcontroller via an RF signal, it is not sufficient to just add an RF receiving circuit unit that has, for example, an antenna and a UART interface, but rather a large-scale modification that replaces everything, including the microcontroller, is required.